1. Field of the Invention
The present invention relates to a printing apparatus that uses an optical sensor to detect a print position adjusting pattern printed on a printing medium and which acquires adjustment values used to adjust print positions on the basis of the results of the detection, as well as a method of setting print position adjustment values, and a printing method.
2. Description of the Related Art
In the prior art, print registration (print position adjustment) in a printing apparatus of this kind is ordinarily carried out as described below. For example, in reciprocative printing, when print registration is executed between a forward scan (forward printing) and a backward scan (backward printing), the forward and backward scans are used to print ruled lines on a printing medium as a print position adjusting pattern. When the ruled lines are printed, print timings between the forward scan and the backward scan are adjusted to vary relative print conditions. Further, if a plurality of heads are used, the print registration between the print heads is carried out by using the plurality of print heads to print ruled lines on a printing medium as print position adjusting pattern. When the ruled lines are printed, print timings between the print heads scan are adjusted to vary relative print conditions.
A user or the like observes the results of such printing to select the ruled line printed under print conditions resulting in the most appropriate print position. Then, on the basis of the print conditions under which the ruled line was printed, the print conditions for print registration are set for a printing apparatus or host computer as print position adjustment values. However, such a conventional method of print registration requires the user or the like to check the results of printing to select and set registration conditions. This is cumbersome.
Thus, Japanese Patent Laid-open No. 10-329381 describes a technique to use an optical sensor to read a print position adjusting pattern. Specifically, in connection with a first and second prints (prints resulting from a forward and backward scans, respectively, or prints obtained using a plurality of heads) as print registration targets, print position adjusting patterns having different amounts of deviation in relative print position are printed on a printing medium. Then, an optical sensor composed of a light emitting section (commonly LEDs) and a light receiving section (commonly phototransistors) is used to measure optical characteristics of the printed adjusting patterns such as a reflection density. Then, on the basis of the measurements, conditions for the print registration between the first and second prints are determined.
Further, in printing apparatuses capable of printing colored images in multiple colors, print agents for tones such as cyan, magenta, and yellow are commonly used in addition to black. Moreover, in recent years, there have been printing apparatuses using a light cyan or light magenta ink in order to reduce the granular impression of dots formed when the ink impacts a printing medium. A technique has also been proposed which favorably measures the optical characteristics of print registration patterns (print position adjusting patterns) formed using the plurality of print agents having the different tones (Japanese Patent Laid-open No. 2001-105635). Specifically, a color filter is provided in a light emitting section of an optical sensor to increase an S/N ratio for parts in which dots are formed and parts in which no dots are formed, when the optical characteristics are measured.
These techniques enable the print registration to be easily carried out without troubling the user. However, the printing apparatus using print agents having different tones require a light source with a large wavelength region which operates as the light emitting section of the optical sensor, a color filter that restricts the wavelength region, and a mechanism that correspondingly controls the switching of the color filter. This disadvantageously increases costs and the size of the apparatuses.